Research project

The first axis of my research project is dedicated to the experimetal studies of granular materials properties.
A granular material is a conglomeration of discrete solid particles. This material can be separated in two
categories : cohesive and non-cohesive. Indeed, the humidity, the electrostatic charges and
the Van der Waals interactions induce some cohesion between the grains. When the weight of one grain is
higher than the cohesive forces, the material is non-cohesive. These materials have been intensively studied
during the last decades because of the rich variety of their physical properties. On the other hand, if the
cohesive forces are higher than the weight of one grain, these forces will strongly modify the properties of the
pile. Among these cohesive granular materials, powders are used in many research domains : chemistry,
pharmacy, engineering... Nowadays, the processes used for the manipulation of powders are mainly based on
empirical knowledge. However, the complexity of the methods used in these research domains induce the
necessity of more rigorous knowledge of these materials. Therefore, a fundamental study of cohesive powders is
essential.

The difficulty to quantify and to control cohesion between the grains of a powder makes their experimental
study very complex. During our previous research, we have developed a controlled cohesive granular material. In
this controlled system, the cohesion between the grains can the tuned easily. This controlled material is made
of spherical ferromagnetic beads placed in an adjustable magnetic field. This system have been used
during my thesis to study the influence of the cohesion on the volumic fraction of a pile (Picking the Packing, Research Highlights in Nature 450, 588 (2007)).

My present research project includes a second axis dedicated to the study of self-assembly processes leading to the formation of mesostructures. Mesostructures
are microscopic (typically from 100 nanometers to 100 microns) architectures with complex arrangements which confer them remarkable physical properties. Static and dynamic properties
of such structures are investigated using model systems of Soft Matter. This activity is based on expertise acquired during my experimental works on collective motions, and patterning
in granular materials. These self-organization processes take place in assemblies of micro and nano particles placed in an external field (magnetic and/or electric) and
submitted to geometrical, mechanical, capillary and hydrodynamic constraints. In order to identify and to control the relevant self-assembly processes, the interactions between the particles
have to be studied precisely. With a better fundamental understanding of these interactions, the self-organization processes will be obtained through a bottom-up method
instead of the classical empirical methods. Then, we will be able to improve the long-range organization in mesostructures, catalyst, porous materials, sintered materials…
Moreover, future studies will be dedicated to reversible self-organized systems where the order could be modified in order to obtain smart reconfigurable materials.

To obtain more details about my works concerning granular materials, see the topic  The physics of sandpiles 
in the Reflections website of the University of Liege.

I am involved in the new platform Aptis dedicated to powder characterization.
I am working on the development of new measurement apparatus dedicated to the characterization of powder flow properties.

6. Linking compaction dynamics to the flow properties of powders
G. Lumay, C. Bodson, L. Delattre, O. Gerasimov and N. Vandewalle
Appl. Phys. Lett.
89, 093505
(2006)The authors have investigated the flow properties of powders by using two classical techniques based on the shear stress measurements and the count of intermittent avalanches, respectively. Results are compared with measurements of the compaction dynamics. Strong correlations are evidenced between compaction relaxation parameters and free flow characteristics. Those correlations are given by semiempirical laws based on physical arguments. This work opens perspectives in powder technology and the knowledge on granular matter.
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